<!DOCTYPE html>
<html lang='en'>

<head>
    <meta charset='UTF-8'>
    <meta http-equiv='X-UA-Compatible' content='IE=edge'>
    <meta name='viewport' content='width=device-width, initial-scale=1.0'>
    <title>Document</title>
    <script src='../../vue.js'></script>
</head>

<body>
    <div id='app'>
        <button @click="isHot = !isHot">改变天气</button>
        <h1>今天的天气真{{isHot?"热":"冷"}}</h1>
        <img :src="url" alt="">
    </div>
    <script>
        Vue.config.productionTip = false;
        const vm = new Vue({
            el: '#app',
            data() {
                return {
                    isHot: true,
                    url: ""
                }
            },
            //watch配置项
            watch: {
                //监听isHot属性
                isHot: {
                    //当被监听的isHot发生改变的时候,handler函数就会执行
                    handler(newValue, oldValue) {
                        console.log("handler", newValue, oldValue);
                        //根据当前的值 去修改url的地址
                        this.url = newValue ? "./re.webp" : "./leng.gif"
                    }
                }
            }
        })
    </script>
</body>

</html>